The world where it all goes down. Andra is, for future surprises (plus to make it easier for characters to fit into the setting), largely undefined. However, to keep things from going completely wonky, there are some things to keep in mind. Most prominent being:
Andra itself is a medieval fantasy-based world.
As such, the population consists of magic-users. They have next to zero knowledge of technology and find it, as well as the people falling out of the sky, rather bizarre.
Next important thing to know? Over ninety percent of the original population is either dead or infected by a plague that turns the infected into a mindless killing machine. They're still alive, but all memory and reason is gone. They live only to slaughter and devour anyone or thing that isn't part of their own number. What caused this disease or how it spread is mostly unknown, but a vaccine was created to prevent any new victims. Finding a cure... that's another story entirely.